Choosing The Correct Presentation; The Malvern Presentation Grid - Malvern Mastersizer Series Getting Started

C H A P T E R 5
Remember - unless you definitely know that the result graph will be of a
particular shape always use the polydisperse model.

Choosing the correct presentation

As stated in earlier chapters the Mastersizer uses the Mie theory to calculate the
size of your sample. The Mie theory requires some knowledge of the optical
characteristics of the sample and the medium it is dispersed in - in particular their
refractive indices. This information is used to calculate a predicted scattering
pattern that the sample would generate when the analyser beam is passed through
it. This predicted scattering pattern is known as a presentation.
The choice of presentation can be one of the most difficult decisions to make
when using the Mastersizer. Saying this, if you are in any doubt you can use one
of the default presentations as these have been chosen to give a "middle of the
road" setting and in most situations this is more than adequate. It should be noted
that even if you only use the default presentations you would still get more
accurate results when measuring small particles than using an instrument that
only uses the Fraunhofer theory.
If however you decide you need a more accurate result then you can use a
presentation that is more closely matched to your sample. The Mastersizer system
is supplied with many pre-calculated presentations based on the "Malvern
presentation grid".

The Malvern presentation grid

The Malvern presentation grid is a convenient method of labeling presentations.
The presentation is labeled by a four character code of the form "3OHD".
The presentation grid is shown on the next page - refer to this grid when reading
the next section, which which discuses its contents.
The first character is a number representing the instrument you are using. If you
have a Mastersizer X then all your presentations will begin with 2 (for example
2OHD) or, if you have a Mastersizer S then all presentations will begin with 3
(for example 3OHD). In the following section the codes for the Mastersizer S (3)
will be used in the examples.
The second character represents the real refractive index of the particle relative to
that of the dispersant. If your particle and dispersant has a relative real refractive
index of 1.45 then the second character will be R, if it has a value of 1.005 then
the second character will be F etc. The values within the grid have been carefully
P a g e 5 . 3
G E T T I N G S T A R T E D